Polycyclic hydrocarbons are strongly suspected of being a major cause of cancer in human beings, especially of lung cancer, which is now the leading cause of all cancer deaths in the United States. Our research is designed to further our understanding of the metabolism of polycyclic hydrocarbons, especially benzpyrene, and the binding of reactive metabolites to DNA --both key steps in the initiation of tumors by these compounds. In addition, it seems quite clear that findings with polycyclic hydrocarbons will have great relevance to the toxicity and carcinogenicity of other xenobiotics as well. There are a number of novel contributions in our research. Examples of these include the use of intact, isolated cells to study xenobiotic metabolism under near in vivo conditions; the identification of new enzymes involved in xenobiotic metabolism (the microsomal glutathione S-transferases); the development of a new fluorescence method for studying the binding of benzpyrene metabolites to DNA; and characterization of a new type of inducer of drug-metabolizing systems, trans-stilbene oxide.